Chemistry Reference
In-Depth Information
●
Refrigerants.
Solid carbon dioxide (dry ice) is used
for refrigerating ice cream, meat and soft fruits. It
is used for this purpose because it is colder than
ice and it sublimes (p. 5), and so it does not pass
through a potentially damaging liquid stage.
●
Special effects.
Carbon dioxide is used to create
the 'smoke' effect you may see at pop concerts and
on television. Dry ice is placed in boiling water and
it forms thick clouds of white 'smoke' (Figure 1.9,
p. 5). It stays close to the fl oor due to the fact that
carbon dioxide is denser than air.
●
Heat transfer agents.
Carbon dioxide gas is used
for transferring heat in some nuclear power stations.
Question
1
List the important uses of carbon dioxide and for each use you
have given in your answer explain why carbon dioxide is used.
Properties of carbon dioxide gas
Physical properties
Carbon dioxide is:
●
a colourless gas
●
sparingly soluble in water
●
denser than air.
Laboratory preparation of carbon
dioxide gas
In the laboratory the gas is made by pouring dilute
hydrochloric acid on to marble chips (CaCO
3
).
calcium + hydrochloric → calcium + water + carbon
carbonate acid chloride dioxide
CaCO
3
(
s
) + 2HCl(
aq
) → CaCl
2
(
aq
) + H
2
O(
l
) + CO
2
(
g
)
A suitable apparatus for preparing carbon dioxide is
shown in Figure 13.16.
Chemical properties
●
When bubbled into water it dissolves slightly
and some of the carbon dioxide reacts, forming
a solution of the weak acid carbonic acid which
shows a pH of 4 or 5.
water + carbon dioxide
carbonic acid
H
2
O(
l
) + CO
2
(
g
)
H
2
CO
3
(
aq
)
●
It will support the combustion only of strongly
burning substances such as magnesium. This
burning reactive metal decomposes the carbon
dioxide to provide oxygen for its continued
burning in the gas. This reaction is accompanied by
much crackling (Figure 13.17).
*
carbon
dioxide
dilute
hydrochloric
acid
water
marble
chips
* If dry gas is required, then it is passed through concentrated
sulfuric acid (to dry it) and then collected as shown below
carbon *
dioxide
CO
2
CO
2
concentrated
sulfuric acid
Figure 13.17
When magnesium burns in carbon dioxide gas, magnesium
oxide (white) and carbon (black) are produced.
Figure 13.16
Preparation and collection of carbon dioxide gas.
